This invention is concerned with the production of titanium dioxide which is characterized by recovery of reusable H.sub.2 SO.sub.4, high pure Fe oxide and hydroxide and fractional recovery of Mn, V and Cr, etc., from FeSO.sub.4.nH.sub.2 O and waste acid of 20 - 40% H.sub.2 SO.sub.4 containing abundant heavy metallic ions, which are by-products of the production of TiO.sub.2 by dissolution of Ti raw materials, such as, ilmenite, steel production slag, such as, electric furnace slag, convertor slag with H.sub.2 SO.sub.4.
In the conventional production of TiO.sub.2 using H.sub.2 SO.sub.4, the required amount of 98% H.sub.2 SO.sub.4 per 1 ton of TiO.sub.2 product is 3.5 to 4.2 tons. Nevertheless, an economical treatment of FeSO.sub.4.nH.sub.2 O and waste acids produced in abundance as by-products after the separation of Ti compounds by the hydrolysis process has not been found and the practice of retaining or discarding them in the untreated form has given rise to serious pollution problems. This invention has been developed to overcome the faults of the conventional production process described above.